The car was being shipped from a race track in Nuremburg, Germany, to Crewe, and had been placed in the back of a container lorry.
The men, who claimed to be Iraqis, were arrested in the French port of Calais as they tried to make it across the Channel to Dover in the supercar.
Officers from the UK Border Agency equipped with carbon dioxide detectors spotted high readings inside the lorry.
When they opened it they found the four grinning migrants sitting in the front and back seats of the Bentley, which has a top speed of more than 200 mph.
UKBA's director, Tom Dowdall, who heads operations in northern France, said: “It's important we stop would-be illegal immigrants before they reach the UK.
"That's why we've got hundreds of British immigration officers based at ports in France and Belgium.
“Last year we searched over 1m lorries and prevented 18,000 foreign nationals from crossing the English channel without permission.”
As well as visual checks of vehicles, officers also use heartbeat detectors, carbon dioxide machines and sniffer dogs to find stowaways.
The alleged Iraqi migrants were arrested on Saturday and are currently in custody in France.